The design of luminaires such as outdoor luminaires, e.g. street lighting, traffic lights, and so on, is typically mandated by standards to ensure that such luminaires comply with the applicable health and safety regulations. Such luminaires may be subdivided into the following classes.
Class I luminaires, which are electrically insulated and provided with a connection to earth in order to protect exposed metal parts that become live, e.g. in case of electrical insulation failure.
Class II luminaires, which are designed such that protection against electric shock does not rely on basic electrical insulation only.
Class III luminaires, for which protection against electric shock relies on the so-called supply at Safety Extra-Low Voltage (SELV) in which voltages above SELV (max. 50V AC RMS) are not generated.
Where luminaires are mounted on electrically insulating structures, e.g. wooden poles, insulating mounting wires or the like, connection to ground may not be feasible, such that Class II luminaires often are used in such circumstances, e.g. when replacing a traditional luminaire with a solid state lighting, e.g. LED-based, luminaire, for example to reduce maintenance needs for the luminaire owing to the excellent lifetime characteristics of solid state lighting-based luminaires as well as to reduce energy costs owing to the excellent energy consumption characteristics of such luminaires. Unfortunately, many luminaires (and in particular Class II luminaires) are particularly vulnerable to common mode surges, e.g. caused by an unforeseen electrical discharge such as a lightning strike, as such surges can negatively impact the lifetime of the active circuit components, e.g. one or more driver circuits and/or one or more light engines, of the luminaire. Such common mode surges for example may occur due to the presence of parasitic capacitances in the luminaire. For example, a parasitic capacitance may exist between copper tracks and the aluminium substrate of a metal core printed circuit board (MCPCB), which can provide an undesired electrical path in case of a surge event.
Therefore, there exists a need for some form of surge protection in such luminaires. However, the widely applicable luminaire standard IEC 60598-1 prevents the use of overvoltage protection devices inside a luminaire to ensure common mode protection. KR 2012/0092843 A discloses a substrate for an LED lighting device having an electromagnetic shielding function to prevent the damage of an inner lead of LEDs by discharging and bypassing electromagnetic energy through a ground pattern. This however cannot be used in Class II luminaires due to the absent ground connection in such luminaires.